AMBER Archive (2007)

Subject: Re: AMBER: CONFIGURATION FILE FOR OXALATE C2O4^2-

From: Eduardo Mendez (pckboy_at_gmail.com)
Date: Tue Sep 18 2007 - 18:41:33 CDT

Thanks for the advice regarding the Mulliken vs RESP charges, I was
trying so hard to solve the software issues that
in my mind I just wanted to plug in some numbers . . .

Eduardo
Jiri Sponer wrote:
> I agree with Ilyas:
>
> Mulliken charges are essentially useless, being extremely
> method and basis set dependent. (Changing marginally one of the inner
> s basis function exponent on Mg2+ (fully hydrated and bound to a ligand)
> can change the calculated Mulliken value on Mg by 0.3 e, despite that
> this change of AO does not change any real property of the system
> by even 0.001 %....
>
> You can use constraints, if you need to impose some geometry
> restrictions. Gaussian is however the best code for geometry optimizations.
>
> Jiri
>
>
> s orbital exponent on Mg2+
>
>> Dear Eduardo,
>>
>> I wonder why you wanted to get the Mulliken charges. Did you try to follow
>> the resp protocol to get the RESP charges?
>>
>> On Mon, 17 Sep 2007, Eduardo Mendez wrote:
>>
>>
>>> As Shakespeare said sometime in a dream of mine"Whats on an
>>> approximation, whatever else its basis set it would smell as sweet (he
>>> may have said that about aromatic compounds)"
>>>
>>> I tried a different program and got Mulliken charges, the question
>>> however remains open, as
>>> I do not know to what degree my calculations will be accurate. If anyone
>>> knows something about
>>> the mischievous Oxalate let me know.
>>>
>>> Eduardo
>>> Eduardo Mendez wrote:
>>>
>>>> Greetings Amber users
>>>>
>>>> I was wondering if anyone could share the amber parameter files for
>>>> oxalate. I did gaussian calculations to get the mulliken charges,
>>>> however, to my dismay, gaussian gives me an isomer, which
>>>> is not in the planar conformation one would expect it to be :(
>>>> Any idea were can I find a library site other than
>>>> http://pharmacy.man.ac.uk/amber/ ???
>>>>
>>>> Thanks in advance
>>>>
>>>> eduardo
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>>>
>> --
>> Ilyas Yildirim
>> ---------------------------------------------------------------
>> = Department of Chemistry - =
>> = University of Rochester - =
>> = Rochester, NY 14627-0216 - Ph.:(585) 275 67 66 (Office) =
>> = http://www.pas.rochester.edu/~yildirim/ =
>> ---------------------------------------------------------------
>>
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